EMERGY SYNTHESIS 5: Theory and Applications of the Emergy Methodology

Proceedings from the Fifth Biennial Emergy Conference, Gainesville, Florida

Edited by Mark T. Brown University of Florida Gainesville, Florida

Managing Editor Sharlynn Sweeney University of Florida Gainesville, Florida

Associate Editors Daniel E. Campbell US EPA Narragansett, Rhode Island

Shu-Li Huang National Taipei University Taipei, Taiwan

Enrique Ortega State University of Campinas Campinas, Brazil

Torbjorn Rydberg Centre for Sustainable Agriculture Uppsala, Sweden

David Tilley University of Maryland College Park, Maryland

Sergio Ulgiati Parthenope University of Napoli Napoli, Italy

December 2009 The Center for Environmental Policy Department of Environmental Engineering Sciences University of Florida Gainesville, FL

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Emergy Evaluation of Water Management in the Florence Area

Federico M. Pulselli, Riccardo M. Pulselli, Nicoletta Patrizi and Nadia Marchettini

ABSTRACT

The paper presents the results of a project on the Province of Florence (Italy), investigating the availability and use of water resources by emergy evaluation. The study is devoted to the analysis of the watershed of the Sieve River, tributary of River Arno that feeds Florence and its surroundings. Along the river an artificial basin has been created by means of the Bilancino dam to preserve water quantity and quality, and to protect the Florentine area from dangerous periodical inundations. Different specific emergies of water can be identified along the course of the river, especially before and after the Bilancino dam. The aqueduct system of the province of Florence is fed by several rivers and torrents. Here we consider Stura, Sieve and Arno rivers. It is fragmented and divided into many subsystems, slightly interacting with each other. Hence, different systems of extraction and distribution of water are chosen on the basis of their dimension, type and location, and evaluated in order to calculate the specific emergy of water in different infrastructural contexts. The emergy investment necessary to implement different water management strategies is evaluated, focusing on the role and use of resources under a sustainability viewpoint.

INTRODUCTION

Water resources have been the core of the development of every process of civilization. Mankind has long tried manners to capture, store, clean and distribute fresh water resources as well as to reduce its vulnerability. Agriculture and industrial activities as well as urban development are made possible by the presence of water and require the implementation of water management systems (Gleick, 2000). From the environmental viewpoint, water management means to reduce pumping from natural storage, reintroduce water as near as possible to its extracting zones and with characteristics as similar as possible to natural ones (Fugaro et al., 2002). Furthermore, according to sustainability criteria, also environmental values and social and cultural implications of human activity have to be involved into the decision-making process, particularly in regard to long-term effect (Helström et al., 2000). This paper presents the results of an environmental assessment of water in the Sieve watershed in the Province of Florence (Italy). An emergy based environmental accounting system (Odum, 1988, 1996) has been implemented. Emergy evaluation takes into account all material and energy flows necessary to obtain a certain product (in this case, water). Emergy can be used to evaluate different aspects of the study of water systems: properties and peculiarities, availability, conservation and sustainable use. See, for example, Odum, 1996 and Odum and Arding, 1991 for the evaluation of chemical potential energy and geopotential energy of water. Fugaro et al., (2002) and Vassallo et al. (2006) presented the results of emergy evaluation of two watershed systems in Italy. Other assessments of water systems and watershed management were also performed through emergy analysis by Odum et al. (1997), Romitelli (2005), Tilley and Brown (2006), Blancher et al. (2007), Agostinho et al. (2008), and Chen et al. (2009). Emergy has been also used to account for the impact of infrastructures

355 necessary to manage water (like dams or rivers diversions) (Brown and McClanahan, 1996, Martin, 2002; Kang & Park, 2002), and the metabolism of rivers (Chen et al., 2009). A dissertation on the value of water and the allocation of water resource at different geographical scales is reported in Buenfill (2001). The analysis presented here has been divided into two parts: the first one takes into account the inputs that feed the flow of water at a given point of the river; the second one takes into account the inputs that support drinkable water production and distribution. The emergy evaluation of water in the river gives an estimation of the work of the ecosystem in making water “naturally” available in different points of the river. This value, expressed in terms of specific emergy of water, is then used, together with the value of all other inputs (e.g. the aqueduct system), to calculate the environmental cost of providing water to the finals consumers. Different site-specific values of emergy per unit mass are calculated and discussed.

MATERIALS AND METHODS

Sieve River is the main right tributary of the Arno River, that feeds the city of Florence and its surroundings. It can be considered as a torrent since it alternates low and high flows of water. Along the river, an artificial basin was created by means of a dam in order to preserve water quantity and quality and protect the Florentine area from possible dangerous floods. In fact, in 1966 a dramatic flood hit the city causing victims and enormous damages. This artificial basin, called Bilancino lake and located in the area of an ancient Pleistocene lake, has an area of 5 km2 and stores 84x106 m3 of water (ARPAT, 2005).

River Stura Stura plant

River Sieve (Sieve Alta)

Bilancino Bilancino DAM lake

River Sieve

Anconella plant Pontassieve plant

River ARNO

Figure 1. The area of analysis: River Sieve watershed (as a portion of the larger Arno watershed) in Tuscany, Italy. Specific emergies of water along the rivers of the area – Stura, Sieve and Arno – were calculated (white circles). Specific emergies of water distributed were calculated for three different plants (Stura, Pontassieve and Anconella plants).

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The dam was built after some decades of political struggles. It is mainly made by 2,000,000 m3 of natural materials locally available, such as diabasic rockfill, limestone rockfill, gravel, sandstone and clay, with an expected life of 200 years. The contribution of reinforcing concrete was considered as negligible in the emergy analysis. Figure 1 shows the area under study, namely river Sieve watershed and a portion of the course of river Arno. Investigation was conducted in order to assess the value of water along the course of the rivers of the area. Four white circles represent the points where the specific emergy of water was calculated: Two points are along the river Sieve (upstream and downstream of Bilancino lake, respectively); two more points are along the river Stura (upstream of the lake) and along the river Arno (in the city of Florence). The choice of the points was due to two reasons: (a) the presence of the Bilancino lake and the dam, that contribute to manage the flow of water and affect its emergy value; (b) the structure of local water distribution network which is composed by several aqueducts of different size (in terms of infrastructure and water collected and distributed), slightly interacting with each other and fed by different points of water extraction. For these reasons, since water has not the same environmental value along the course of a river, the analysis of aqueduct systems was performed in the proximity of points of the rivers previously analyzed (water collection points). In fact, three of the four white circles in Figure 1 coincide with plants/aqueduct systems, namely Stura, Pontassieve and Anconella plants (represented by white boxes placed upon circles). The energy diagram is shown in Figure 2. It provides a general overview of the system and its main components. The boundaries of the system are represented by the larger rectangle. The grey box represents Sieve watershed, including the tributaries of river Sieve, the dam and Bilancino lake located along the course of the river. These components, together with natural environmental inputs (sun, rain, wind, geothermal heat and basic flow/spring water), affect the value of water. Downstream of Bilancino Lake, river Sieve drains into Arno. Water in the rivers is represented by storages since it has to be maintained. Along the course of water, from Sieve river to Bilancino lake and Arno river, three points of water withdrawing are represented as splits. Arrows going to the aqueduct system represent all the inputs (including water collected) necessary to purify and distribute water. The diagram, from left to right, describes the course of water in all its phases, represented in series: water flows from a reservoir to another and is withdrawn at different points. In each point of the watershed, water assumes different environmental values. In calculating the emergy value of water in different points, natural components as well as anthropic infrastructures and energy (goods and services) necessary to make water available were taken into account. In particular: the dam contributes to maintain the flow of water and it was included in the analysis in terms of materials and costs; the aqueduct system produces and distributes drinkable water to people and was considered in terms of the mass and energy involved in all the processes (electricity, human work, machineries, pipes, concrete, sand and money). Water is distributed to people, who pay money for this service.

RESULTS AND DISCUSSION

Emergy evaluation of water in the rivers

The presence and availability of water along the course of the rivers depend on natural components and, downstream of Bilancino lake, on the presence of the dam, as a structural component of the system. The points investigated are represented by white circles in Figure 1. Sun, rain, geothermal heat and the basic flow (as proxy for spring water) were considered as input flows. The dam was also taken into consideration by accounting for the contribution of building materials and costs (construction and maintenance costs). All data were collected from official local authorities dealing with the management of the area (Autorità di Bacino del Fiume Arno, Regione Toscana, ARSIA, Publiacqua S.p.a.). The output of each subsystem is the amount of water that flows

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spring Goods & water Services

sun geoth.heat rain wind materials sediments nutrients sediments water in nutrients river Sieve water in & its tributaries dam river Arno people Bilancino € lake & cities

aqueducts € water collection drinking water production plant drinking water distribution network loss of water

loss of sediments

Figure 2. Energy diagram of the system under study. The grey box represents Sieve watershed and Bilancino lake; downstream of Bilancino, Sieve river drains into Arno; the splits correspond to water withdrawn by the aqueduct system.

every year in each point of the river. Raw data (mass quantities) have been reported and processed as in Tables 1, 2, 3 and 4. References for emergy per unit used in the tables are: (1) Odum, 1991; (2, 3) Odum et al., 2000 (folio 1); (4) Brown & Arding, 1991 (updated to 2000 to make all transformities consistent with the 15.83 E24 sej/year baseline); (5, 6) Odum, 2000 (folio 2); (7, 8, 9) Odum, 1996 (updated to 2000); (10) Pulselli et al., 2006; (11, 12, 13, 14) this study. For computations, see notes to Table 3 in appendix. Figure 3 shows the four values of specific emergy at the points in Stura and Sieve Alta, upstream of Bilancino lake, and Pontassieve and Anconella, downstream of Bilancino lake.

Table 1. Calculation of specific emergy of water of river Stura. Item Input Unit Reference Emergy per unit Emergy per yr (eM. per unit) (sej/unit) (sej/year) 1 Sunlight 1.92x1017 J (1) 1 1.92x1017 R 2 Rain 5.29x1013 g (2) 1.45x105 7.67x1018 R 3 Geothermal heat 1.06x1014 J (3) 1.20x104 1.28x1018 R 4 Spring water 1.02x1012 g (4) 3.40x105 3.48x1017 R Total emergy 9.30x1018 5 Water flow - Stura 4.06x1013 g (11) 2.29x105

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Table 2. Calculation of specific emergy of water of river Sieve (Sieve Alta). Item Input Unit Reference Emergy per unit Emergy per yr (eM. per unit) (sej/unit) (sej/year) 1 Sunlight 1.54x1017 J (1) 1 1.54x1017 R 2 Rain 4.23x1013 g (2) 1.45x105 6.14x1018 R 3 Geothermal heat 8.50x1013 J (3) 1.20x104 1.02x1018 R 4 Spring water 8.18x1011 g (4) 3.40x105 2.78x1017 R Total emergy 7.44x1018 5 Water flow - Sieve Alta 3.15x1013 g (12) 2.36x105

Table 3. Calculation of specific emergy of water of river Sieve in Pontassieve. Item Input Unit Reference Emergy per unit Emergy per yr (eM. per unit) (sej/unit) (sej/year) 1 Sunlight 3.62x1018 J (1) 1 3.62x1018 R 2 Rain 8.15x1014 g (2) 1.45x105 1.18x1020 R 3 Geothermal heat 2.00x1015 J (3) 1.20x104 2.40x1019 R 4 Spring water 1.93x1013 g (4) 3.40x105 6.55x1018 R 5 Dam 1.66x1020 5a Diabasic rockfill 4.90x109 g (5) 9.50x109 4.65x1019 N 5b Limestone 9.34x109 g (6) 9.50x109 8.87x1019 N 5c Gravel 2.58x109 g (7) 1.68x109 4.33x1018 N 5d Sand 2.85x109 g (8) 1.68x109 4.79x1018 N 5e Clay 4.63x109 g (9) 4.10x109 1.90x1019 N 6 Costs (building, maintenance) 2.10x106 € (10) 1.40x1012 2.94x1018 F Total emergy 3.15x1020 7 Water flow - Pontassieve 3.22x1014 g (13) 9.78x105

Table 4. Calculation of specific emergy of water of river Arno (in Anconella). Item Input Unit Reference Emergy per unit Emergy per yr (eM. per unit) (sej/unit) (sej/year) 1 Sunlight 1.76x1019 J (1) 1 1.76x1019 R 2 Rain 3.88x1015 g (2) 1.45x105 5.63x1020 R 3 Geothermal heat 1.23x1016 J (3) 1.20x104 1.47x1020 R 4 Spring water 1.85x1013 g (4) 3.40x105 6.30x1018 R 5 Dam 1.66x1020 5a Diabasic rockfill 4.90x109 g (5) 9.50x109 4.65x1019 N 5b Limestone 9.34x109 g (6) 9.50x109 8.87x1019 N 5c Gravel 2.58x109 g (7) 1.68x109 4.33x1018 N 5d Sand 2.85x109 g (8) 1.68x109 4.79x1018 N 5e Clay 4.63x109 g (9) 4.10x109 1.90x1019 N 6 Costs (building, maintenance) 2.10x106 € (10) 1.40x1012 2.94x1018 F Total emergy 8.82x1020 7 Water flow - Anconella 1.62x1015 g (14) 5.44x105

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9.78

10

9

8 sej/g 5 7 5.44 6

5

4 2.29 2.36 3

2 Specific emergy - 1x10 1

0 Stura Sieve alta Sieve Pontassieve Arno Anconella

Figure 3. Comparison of specific emergies (1x105 sej/g) of water in the rivers.

Specific emergies of water calculated for the Stura and Sieve Alta are about the same (2.29x105 sej/g and 2.36x105 sej/g respectively). The portions of watershed related to them are similar and the two rivers are fed by similar types of inputs. In addition, both systems are not markedly affected by anthropogenic inputs. The specific emergy of water obviously increases along river Sieve after the Bilancino dam (9.78x105 sej/g in Pontassieve) since the emergy of the dam is included: the amount of inputs that are necessary to provide that quantity of water is higher. This includes the service of regulating the river flow, preventing dangerous situations downstream. In Pontassieve, river Sieve drains into river Arno and after that point the specific emergy decreases again (5.44x105 sej/g in Anconella, in the city of Florence) because the weight of the dam is now referred to a higher quantity of water. In fact, the whole Arno watershed is the target of the investment: the Bilancino dam was built with several purposes, including to regulate water in river Sieve and prevent floods of river Arno. The specific emergy of water at Anconella is thus lower than that calculated in Pontassieve. This result shows that the dam project seems a good step towards the sustainable management of water resources. The dam is built with non renewable materials, but its purpose is to preserve water and facilitate its renewability in the long run. This condition seems in line with Herman Daly’s “quasi-sustainability” principle dealing with non-renewable resources (Daly, 1990). He stated that “the category of non- renewable resources cannot be maintained intact short of non-use (and if they are never to be used then there is no need to maintain them for the future!). Yet it is possible to exploit non-renewables in a quasi-sustainable manner by limiting their rate of depletion to the rate of creation of renewable substitute”. In this case, all the materials used to build the dam are local non-renewable resources (even if they are not exhausted or destroyed but simply moved from their original position); at the same time, the dam provides a regular water flow during the year in such a way that it is used in a renewable way. This is a re-interpretation of Daly’s “quasi-sustainability” principle, since water is not a renewable substitute of non-renewable materials used to build the dam, but the construction of it represents an example of rational use of non-renewable resources to enhance the capture of a renewable one. From a theoretical point of view, Bastianoni et al. (2009) presented a possibility for pursuing a prosperous way down based on the use of non-renewable resources to improve systems’ capacity to exploit renewable resources permanently.

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Emergy evaluation of water distributed

The ecosystem effort to provide water in the rivers (plus the fundamental contribution of the dam), is now complemented by human work and settlements. Three aqueducts different in size, in terms of infrastructure and water distributed, have been analysed. In Figure 1, they are called Stura plant (small mountainous plant that serves about 9000 inhabitants), Pontassieve plant (medium sized plant for 20,000 inhabitants) and Anconella plant (large plant of the city of Florence, 350.000 consumers), and are located in three of the four points where the specific emergy of water was calculated. The value of water that is collected from those points is therefore the specific emergy previously calculated. In particular, Stura plant is fed by water of river Stura (Table 1), Pontassieve plant by water of river Sieve in Pontassieve (Table 3), and Anconella plant by water of river Arno in Anconella (Table 4). The other inputs considered for the assessment of the production and distribution system are: pipelines, electricity, human work, chemicals, concrete for tanks, sand that covers pipelines and steel (pumps). The output of the systems is the amount of water that each plant distributes every year. Data comes from Publiacqua s.p.a. (administrator of the aqueduct, referred to 2007). A mass inventory has been performed and emergy results have been reported in Tables 5, 6, and 7. References for emergy per unit are: (1, 2, 3) this study; (4) Pulselli et al., 2007; (5, 6, 7, 8, 9) Buranakarn, 1998 (updated to 2000); (10) processed by Bastianoni et al., 2005; (11) Pulselli et al., 2007; (12) Buranakarn, 1998 (updated to 2000); (13) Odum, 1992 (updated to 2000); (14) Buranakarn, 1998 (updated to 2000); (15) Ulgiati et al., 1994 (updated to 2000); (16) Odum, 1996 (updated to 2000); (17) Buranakarn, 1998 (updated to 2000); (18, 19, 20) this study. For computations, see notes to Table 6 in appendix. The three plants are different in size, providing different amounts of water. Figure 4 shows that the three specific emergy values of water distributed are similar, with lower value corresponding to larger dimension. Differences in specific emergy are due to different quantities and specific emergies of water in input (collected from different points), different flows of water distributed, and different flows of energy and matter that support each plant. The main emergy flow for Anconella and Pontassieve is water in input (more than 46% and 57%, respectively). Water collected by these two plants has a high

Table 5. Calculation of specific emergy of water distributed by Stura plant. Item Input Unit Reference Emergy per unit Emergy per yr (em. per unit) (sej/unit) (sej/year) 1 Water collected 4.13x1011 g (1) 2.29x105 9.45x1016 R 2 Pipeline Cast iron 3.25x107 g (6) 4.45x109 1.45x1017 F Polyethylene 1.54x107 g (9) 8.85x109 1.36x1017 F Tar 7.11x103 g (10) 3.90x109 2.77x1013 F Steel 3.92x106 g (12) 6.97x109 2.73x1016 F 3 Electricity 4.17x1011 J (13) 2.07x105 8.63x1016 F 4 Chemicals 8.49x106 g (14) 2.65x109 2.25x1016 F 5 Human Labour 9.42x107 J (15) 1.24x107 1.17x1015 F 6 Steel (pumps and tanks) 1.48x106 g (12) 6.97x109 1.03x1016 F 7 Sand Covering cast iron pipes 1.21x108 g (16) 1.68x109 2.03x1017 F Covering polyethylene pipes 5.36x107 g (16) 1.68x109 9.00x1016 F Covering steel pipes 1.77x107 g (16) 1.68x109 2.97x1016 F

Total emergy 8.46x1017 8 Water distributed 2.48x1011 g (18) 3.41x106

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Table 6. Calculation of specific emergy of water distributed by Pontassieve plant. Item Input Unit Reference Em. per unit Emergy per yr (em. per unit) (sej/unit) (sej/year) 1 Water collected 2.19x1012 g (2) 9.78x105 2.14x1018 R (47%) 2 Pipeline Iron 7.18x106 g (5) 2.10x1010 1.51x1017 F Cast iron 5.11x107 g (6) 4.45x109 2.27x1017 F PEAD 1.53x106 g (7) 8.85x109 1.35x1016 F PVC 1.14x107 g (8) 9.86x109 1.12x1017 F Polyethylene 1.33x106 g (9) 8.85x109 1.18x1016 F Tar 5.53x103 g (10) 3.90x109 2.16x1013 F Steel 1.70x107 g (12) 6.97x109 1.18x1017 F 3 Electricity 8.78x1011 J (13) 2.07x105 1.82x1017 F 4 Chemicals 3.16x107 g (14) 2.65x109 8.38x1016 F 5 Human Labour 5.53x108 J (15) 1.24x107 6.49x1015 F 6 Concrete (tanks) 1.48x107 g (11) 3.04x109 4.51x1016 F 7 Sand Covering iron pipes 2.95x107 g (16) 1.68x109 4.96x1016 F Covering cast iron pipes 2.20x108 g (16) 1.68x109 3.69x1017 F Covering PEAD pipes 3.61x107 g (16) 1.68x109 6.06x1016 F Covering polyethylene pipes 2.02x107 g (16) 1.68x109 3.40x1016 F Covering PVC pipes 1.69x106 g (16) 1.68x109 2.84x1015 F Covering steel pipes 7.70x107 g (16) 1.68x109 1.29x1017 F 8 Steel (pumps) 5.33x105 g (12) 6.97x109 3.72x1015 F 9 Brickwork (tanks) 1.91x106 g (17) 3.68x109 7.02x1015 F

Total emergy 3.75x1018 10 Water distributed 1.22x1012 g (19) 3.07x106

specific emergy (9.78x105 and 5.44x105 sej/g, respectively) and is only partially renewable (the dam represents the 52.77% of the emergy value of water in Pontassieve and the 18.84% in Anconella - see tables 3 and 4). On the contrary, water collected from river Stura has been considered completely renewable (just like water calculated for Sieve Alta - see tables 1 and 2), from an emergy point of view, since no anthropogenic input is involved in its production. For Stura plant, the main emergy contribution is due to infrastructure (pipelines, steel and sand are about 76% of total emergy), whereas water in input is only 11% of total emergy. The lower number of final users and their dispersion in this mountainous territory imply a larger investment per unit water. In fact, the amount of purchased emergy necessary for purifying and distributing drinkable water is 3.03x106sej/g. The emergy investment in Pontassieve and Anconella plants is 1.32x106sej/g and 1.35x106sej/g, respectively. The value of specific emergy of water distributed by Stura plant is the highest. Furthermore, specific emergy of water distributed is 14 times higher than specific emergy of water withdrawn from the river Stura. This gap represents the value that must be added in order to provide the service of water distribution in a place where that service is more difficult to be implemented. However, small plants like that on the river Stura are necessary, and it is not possible or convenient to build greater plants in mountain areas to serve a small number of consumers. In contrast, the specific emergy of water distributed by Anconella plant is the lowest one. Anconella plant is an important industrial settlement that meets the need of water of the city of Florence, by processing and distributing a great

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Table 7. Calculation of specific emergy of water distributed by Anconella plant. Item Input Unit Reference Em. per unit Emergy per yr (em. per unit) (sej/unit) (sej/year) 13 5 19 1 Water collected 7.14x10 g (3) 5.44x10 3.89x10 R (81%) 2 Pipeline Asbestos cement 2.18x106 g (4) 3.04x109 6.64x1015 F Iron 3.25x108 g (5) 2.10x1010 6.83x1018 F Cast iron 1.69x109 g (6) 4.45x109 7.51x1018 F PEAD 3.23x103 g (7) 8.85x109 2.94x1013 F PVC 2.05x105 g (8) 9.86x109 2.03x1015 F Polyethylene 6.63x105 g (9) 8.85x109 5.87x1015 F Tar 7.66x102 g (10) 3.90x109 2.99x1012 F Reinforced concrete 6.77x105 g (11) 3.04x109 2.06x1015 F Steel 3.45x106 g (12) 6.97x109 2.40x1016 F 3 Electricity 9.72x1013 J (13) 2.07x105 2.01x1019 F 4 Chemicals 1.48x109 g (14) 2.65x109 3.91x1018 F 5 Human Labour 1.31x1010 J (15) 1.24x107 1.63x1017 F 6 Concrete (tanks) 7.41x107 g (11) 3.04x109 2.25x1017 F 7 Sand Covering asbestos cement pipes 1.77x107 g (16) 1.68x109 2.98x1016 F Covering iron pipes 2.09x108 g (16) 1.68x109 3.52x1017 F Covering cast iron pipes 3.28x109 g (16) 1.68x109 5.52x1018 F Covering PEAD pipes 7.92x105 g (16) 1.68x109 1.33x1015 F Covering polyethylene pipes 3.96x106 g (16) 1.68x109 6.65x1015 F Covering PVC pipes 9.85x103 g (16) 1.68x109 1.66x1013 F Covering reinforced concrete 9.69x106 g (16) 1.68x109 1.63x1016 F pipes Covering steel pipes 4.79x106 g (16) 1.68x109 8.05x1015 F 8 Steel (pumps) 7.20x106 g (12) 6.97x109 5.02x1016 Total emergy 8.36x1019 9 Water distributed 3.33x1013 g (20) 2.52x106

3.41 3.07

sej/g sej/g 3,5 2.52 6 3 2,5

2 1,5 1 0,5

Specific emergySpecific - 1x10 0 Stura plant Pontassieve plant Anconella plant

Figure 4. Comparison of specific emergies (1x106 sej/g) of water distributed by the three plants.

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amount of water. It implies that the investment is referred to a huge amount of final product (drinkable water). In this sense, the Anconella plant seems to be the most efficient, in terms of the amount of resources (expressed in emergy) used per unit product. This is also corroborated by the percentage of water lost during the process: 40% for Stura plant; 43% for Pontassieve plant and more than 50% for Anconella plant. Nevertheless, specific emergy of water distributed by Anconella plant is the lowest one. Specific emergy of water varies along the course of a watershed due to accumulation and integration of meteorological and geological inputs. This “natural value” of water should be taken into consideration together with other contextual elements. In fact, specific emergy of water varies also on the basis of the inputs necessary to purify and distribute drinkable water to people living in different areas. Emergy evaluation has the potential to identify and compare the contribution of many inputs to a production process, highlighting the role of the environmental services supporting human activities.

CONCLUSION

The emergy evaluation performed in this study shows that a careful investigation of all of natural and anthropogenic flows (material and energy) supporting the presence and/or the production of water is important for a sustainable management of water resources within a watershed. We used emergy evaluation to describe the “story” of water along the watershed, according to the trend of specific emergy. Specific emergy reflects the characteristics of a natural system that makes water available in a river. The different values of specific emergy of water produced by different plants depend on the capacity (or efficiency, in terms of the quantity of resources necessary to provide a unit of product) of an infrastructure that distributes drinkable water and on the processes implemented to reach a certain number of end users. Together with other technical parameters, emergy can be used to appreciate how much infrastructure influences these values, also taking into account the conditions of surrounding environment. Emergy can be used as a powerful tool since it provides a deeper knowledge of the watershed (accounting for all flows involved in the production of water by the ecosystem) and helps decision makers to choose the best way for territorial planning and resource management.

ACKNOWLEDGMENTS

The authors would like to thank the Province Administration of Florence and its Environmental Department, for funding the research presented in this paper as well as Publiacqua s.p.a., Autorità di Bacino Fiume Arno and ARPAT for providing information.

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APPENDIX

As sample of calculation, we present notes to Table 3 and 6 to show emergy evaluation of water in the rivers and distributed by plants, respectively.

Notes to table 3 1) Sunlight: Area of Sieve watershed in Pontassieve 8.46x108 (m2) [Autorità di Bacino Fiume Arno, 2001] * insolation 5.36x109 (J/m2/yr) [Geophysical observatory, Italy] * (1-0.2) (% albedo given as decimal) [Henning, 1989]; 2) Rain: Area (see point 1) *mean annual rainfall 0.96 (m/yr) [ARSIA] * water density 1.00x106 (g/m3); 3) Geothermal heat: Area (see point 1) * earth heat energy on area 7.50x10-2 (W/m2)* conversion factor 3.15x107 (J/m2/yr); 4) Spring water: Quantity of water 1.93x107 (m3/yr) [Autorità di Bacino Fiume Arno, 2001] * water density 1.00x106 (g/m3); 5) Dam: 5a) diabasic rockfill: Volume 1.78x105 m3 [Publiacqua s.p.a., personal communication] * diabasic rockfill density 5.50x106 (g/m3) / lifetime 200 yr (our estimation); 5b) limestone: Volume 6.89x105 m3 [Publiacqua s.p.a., personal communication] * limestone density 2.71x106 (g/m3) / lifetime 200 yr (our estimation); 5c) gravel: Volume 3.00x105 m3 [Publiacqua s.p.a., personal communication] * gravel density 1.72x106 (g/m3) / lifetime 200 yr (our estimation); 5d) sand: Volume 4.07x105 m3 [Publiacqua s.p.a., personal communication] * sand density 1.40x106 (g/m3) / lifetime 200 yr (our estimation); 5e) clay: Volume 3.56x105 m3 [Publiacqua s.p.a., personal communication] * clay density 2.60x106 (g/m3) / lifetime 200 yr (our estimation) 6) Costs (building, maintenance): building costs 3.00x108 (€) [Publiacqua s.p.a., personal communication] / lifetime 200 yr (our estimation) + maintenance costs 6.00x105 (€/yr); 7) Water flow in Pontassieve: Annual Sieve flow 3.22x108 (m3/yr) [Autorità di Bacino Fiume Arno, personal communication] * water density 1.00x106 (g/m3); Specific emergy of water in Pontassieve: Total emergy 3.15x1020 sej/yr / water flow Sieve Pontassieve 3.22x1014 g/yr = 9.78x105 sej/g

Notes to table 6 (all data from Publiacqua s.p.a.) 1) Collected water: Water extraction 2.19x106 (m3/yr) [Publiacqua s.p.a., personal communication] * water density 1.00x106 (g/m3); 2) Pipeline: Iron: volume 4.56x101 m3 (pipeline materials are estimated on the basis of data from Publiacqua s.p.a.) * iron density 7.87x106 g/m3 / pipes lifetime 50 yr (our estimation); Cast iron: volume 3.65x102 m3 (our estimation) * cast iron density 7.00x106 g/m3 / pipes lifetime 50 yr (our estimation); PEAD: volume 4.77x101 m3 (our estimation) * PEAD density 1.60x106 g/m3 / pipes lifetime 50 yr (our estimation); PVC volume 4.12x102 m3 (our estimation) * PVC density 1.38x106 g/m3 / pipes lifetime 50 yr (our estimation); Polyethylene volume 7.24x101 m3 (our estimation) * polyethylene density 9.20x105 g/m3 / pipes lifetime 50 yr (our estimation); Tar: weight 2.76x105 g (our estimation) / pipes lifetime 50 yr (our estimation); Steel: volume 1.10x102 m3 (our estimation) * steel density 7.75x106 g/m3 / pipes lifetime 50 yr (our estimation); 3) Electricity: Electricity used 2.44x108 Wh/yr * energy content 3600J/Wh; 4) Chemicals: sodium chlorite 1.87x107 g/yr + sodium hypochlorite 3.87x104 g/yr + flocculant 8.13x104 g/yr + carbon dioxide 4.60x103 g/yr + hydrochloric acid 1.28x107 g/yr; 5) Human labour: Yearly working hours 1.00x103 h/yr * metabolism energy 5.23x105 J/h; 6) Concrete (tanks) Total tanks weight 3.11x109 g / lifetime 75 yr (our estimation); 7) Sand: Covering iron pipes: 2.95x109 g; Covering cast iron pipes: 2.20x1010 g; Covering PEAD pipes: 3.61x109 g; Covering polyethylene pipes: 2.02x109 g; Covering PVC pipes: 1.69x108 g; Covering steel pipes: 7.70x109 g; Lifetime for sand: 100 yr. 8) Steel (pumps): Pumps weigh 8.00x106 g / lifetime 15 yr (our estimation); 9) Brickwork (tanks): Brickwork weigh 1.43x108 g / lifetime 75 yr (our estimation); 10) Water distributed: 1.22x106 (m3/yr) * water density 1.00x106 (g/m3); Specific emergyof water from Pontassieve plant: Total emergy: 3.75x1018 sej/yr / annual water distributed by Pontassieve plant 1.22x1012 g/yr = 3.07x106 sej/g

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